Catalytic patio heater

ABSTRACT

A patio heater is disclosed comprising a cylindrical catalytic heating chamber mounted on a base. The patio heater of the present invention comprises a base to physically support a cylindrical catalytic heater chamber which is mounted inside a fuel vapor cavity. The catalytic heater chamber provides a cylindrical heating zone capable of heating a nearby human form the knee to the face. The fuel vapor chamber surrounds the catalytic heating chamber and acts to accumulate sufficient fuel and air mixture to ignite to provide uniform and sufficient heat to the catalyst surface to attain catalytic ignition on start up. The base offers physical stability for the assembly and storage space for a fuel tank and houses the fuel deliver system and ignitor controls.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for heating a relatively open outdoor space such as a patio. More particularly the invention relates to a catalytic heater which provides for a high proportion of radiant heat per unit of fuel consumed. More particularly the invention relates to a vertically oriented heater which radiates heat to users from the face down to about the knees.

2. Related Information

In outdoor environments where wind can divert convected heat a heater which produces radiant energy is essential. Conventional patio heaters are based upon open flame combustion heating a porous metal structure which radiates heat. Typically the burner is positioned at the top of a pole which is mounted on a base which may or may not house a fuel tank. The burner and radiating metal structure are covered by a dome which protects the burner from the weather and reflects energy from the burner downward to the patio.

The conventional patio heaters have several disadvantages. First, the radiant heat from the glowing metal has a wave length of from 1-3 microns, which is not especially useful for warming cloth or flesh. Second, the heat is generated at a height and must be directed downward which results in a warm head but a cold body—the heat patterns are not uniform. Thirdly, much of the heat is in the form of convected heat (hot air) rather than radiant heat and is lost due to heat rising from the burner and is thus rendered useless for heating.

The conventional catalytic heater comprises a container with four walls and a back with an open front. The open box thus formed is filled with a spacer to create an open volume next to the back. This spacer is made from a porous metal to allow gas permeability. Next a layer of dense ceramic fiber mat is inserted which acts as a thermal insulator and flow distributor. Finally, a low-density ceramic fiber mat which has been coated with platinum is inserted. The contents are held in the box using a wire mesh with large holes. Fuel gas is delivered from an orifice and a fitting on the back of the heater. The fuel fills the cavity and diffuses through the ceramic fiber pad and the platinum coated pad. Air contacts the gas in the pad or at its outer surface. If the outer surface is heated to the temperature required for catalytic ignition the fuel and air mixture will combust flamelessly.

In the conventional catalytic heater the air and fuel are not pre-mixed. However systems wherein some air is pre-mixed (10-20% of the theoretical air) are disclosed in U.S. Pat. Nos. 5,037,293 and 6,470,874

The catalyst in catalytic heaters must be heated to about 250° C. to get catalytic ignition. An electrical heater is typically embedded in the catalytic layer in order to provide the heat for ignition. The ignition starts near the electrical heater and eventually spreads after the catalyst has ignited. The time required for steady state can be long, on the order of ten to twenty minutes. In the case where the fuel and air are pre-mixed and electrical discharge may be used for ignition.

Catalytic heaters in general produce much more radiant energy per unit of fuel consumed and furthermore, the radiant energy is in the wave length of between 1-10 microns, which is the most useful for heating clothing and flesh. The prior catalytic heaters have several disadvantages when used as patio heaters. First, the flat surface directs the heat in only one direction. Second, the time to get to temperature is too long. Third, extensive use of stainless steel or other metal to contain the heater results in high cost and weight. Forth, there is significant heat loss from the rear of the heater.

The object of the present invention is to offer a new and enhanced patio heater which will more efficiently heat a three dimensional volume with lower fuel cost and lower emissions of smog producing chemicals.

SUMMARY OF THE INVENTION

Broadly the present invention is a patio heater comprising a cylindrical catalytic heating chamber vertically mounted on a base. Preferably the catalytic heating chamber is comprised of a low density ceramic pad coated with a highly dispersed oxidation catalyst; a high density ceramic insulating pad; wherein the low density ceramic pad and the high density ceramic pad are rolled together to form a cylinder around the outer surface of a perforated metal cylinder to form a fuel chamber with the high density ceramic pad being located between said low density ceramic pad and the perforated metal cylinder; a cylindrical sleeve around the catalytic heating chamber, said sleeve being formed from expanded metal and having openings of from one-quarter square inch to five square inches with a total open area of from 50% to 90%; and caps covering either end of said catalytic heating chamber, overlapping said sleeve and sealing said fuel chamber. In a preferred embodiment an expanded metal cylinder spaced away from and around said catalytic heating chamber forms a vapor cavity annular to said catalytic heating chamber with the vapor cavity being from one-half inch to two inches in diameter outside the catalytic heating chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an isometric view of one embodiment of the assembled heater of the present invention.

FIG. 2 shows a cross sectional view of the heating area.

FIG. 3 shows a detail of the fuel introduction system.

DETAILED DESCRIPTION

Among the features of the patio heater of the present invention there is a base to physically support a cylindrical catalytic heating chamber which is mounted inside a fuel vapor cavity. The catalytic heating chamber provides a cylindrical heating zone capable of heating a nearby human form the knee to the face. A fuel vapor compartment surrounds the catalytic heating chamber and acts to accumulate sufficient fuel and air mixture to ignite to provide uniform and sufficient heat to the catalyst surface to attain catalytic ignition. The base offers physical stability for the assembly and storage space for a fuel tank. In addition the base also houses the fuel delivery system and ignitor controls.

For a detailed description of one embodiment of the invention the reader is directed to the accompanying figures in which like components are given like numerals for ease of reference.

Referring first to FIG. 1 there is shown an isometric view of one embodiment of the present invention. The protective screen 1 surrounds the cylindrical catalytic heating chamber 110 which contains the fuel vapor compartment 100. Both the protective screen and the catalytic heating chamber are mounted on the base 19 which is a cabinet and also acts as a storage facility for a typical propane gas bottle (not shown). A door 20 allows access to the propane storage facility and for connecting a propane bottle (not shown) to fitting 205 on the catalytic heating chamber 110. Side panels 30 (only one of three shown) enclose the storage facility. The side panels 30 may have vents 31 to allow any leakage from the propane bottle to escape. An electric ignitor button 17 and fuel control knob 14 which controls the feed of gas to the catalytic heating chamber 110 are conveniently mount to base 19. Pilot light assembly 18 is mounted on the face of the base 19 adjacent to heating chamber 110 as described below. Coaster wheels 21 allow the whole assembly to be easily moved when the entire structure is tilted backward using handle 27 which is mounted on cap 28. The cap 28 is attached to the catalytic heating chamber 110 by bolt 25 and nut 28.

Referring now to FIG. 2, the core of the device is the catalytic heating chamber 110. The catalyst pad 6 comprises a low density ceramic fiber pad which is coated with a highly dispersed oxidation catalyst such as platinum, palladium, rhodium or cobalt oxide. When platinum, palladium or rhodium are used the preferred loading is from about 1.0 to 10 wt. % based upon the total weight of the low density pad. When cobalt oxide is used, the preferred loading is form 1 to 20 wt. % based upon the total weight of the low density pad. The low density ceramic fiber catalyst coated pad 6 preferably has a density of from between 1 to 8 pounds per cubic foot. A higher density ceramic pad 7 acts as thermal insulation and flow distributor. The high density ceramic pad 7 preferably has a density of from 8 to 50 pounds per cubic foot. The low density catalyst pad 6, which forms the outer surface of the catalytic heating chamber 110 is placed around the high density pad 7 and the two are rolled together to form a cylinder around the outer surface of a perforated metal cylinder 10, which forms the fuel chamber 100. The high density pad 7 is placed on the cylinder 10 such that the high density ceramic fiber pad 7 is located between the cylinder 10 and the low density catalyst pad 6. The perforated cylinder 10 may be made of sheet metal which has 25 to 70% of its surface as holes of between 0.033 and 0.25 inch diameter. A sleeve 5, formed of expanded metal, surrounds the low density catalyst pad 6, such that the high density and the low density pads are held tightly together between the sleeve 5 and the perforated cylinder 10. The expanded metal sleeve 5 comprises an open area sheet with openings ranging from one-quarter square inch to five square inches with a total open area ranging from 50% to 90%. The top and bottom of the fuel chamber are covered with caps 9 and 8, respectively. The gas is delivered through a tube 101 which is in the center of spacer cylinder 102 on which a diffuser plate 11 made of perforated metal is mounted. The perforated plate acts to prevent too much of the propane fuel, which is heavier than air, from falling to the bottom of the fuel chamber. Outer caps 41 and 12 are used to seal the ends of the ceramic pads to form the catalytic heating chamber which includes the fuel chamber 100, the perforated cylinder 10, the ceramic pad 7, the catalyst pad 6 and sleeve 5. The caps 41 and 12 overlap and seal the catalytic heating chamber including the expanded metal sleeve 5. The caps 8 and 9 are secured to caps 12 and 41 by brads 12 a and 9 a, respectively. An important feature of the embodiment shown is the dimension of the heating chamber. Because it is round (cylindrical) it radiates energy in 360 degrees around its lengthwise axis. The heating chamber's height is 982.6 centimeters which creates a heat flux which reaches approximately from the knee of a human subject to his face at about 5 to 7 feet distance from the heater at a gas flow of about 31,000 BTU's per hour.

In the embodiment shown, a fuel chamber 100 for air and fuel is produced by forming a vapor cavity 100 for the catalytic heating chamber 110. The catalytic heating chamber is centered on the base 19 and surrounded by the protective screen 1 and the cap 22 to form an annular space 103 around the surface of the catalytic heating chamber 110 and is held to catalytic heating chamber by nuts 28 and 29 on bolt 25. When the fuel diffuses through the catalyst, it blends with air in this cavity. When the mixture of the fuel and air are ignited, the heat generated in this cavity is sufficient to raise the temperature of the catalyst pads 6 and 7 high enough (250° C.) to light off catalytic (flameless) combustion. The annulus dimensions between spacer cylinder 102 and the perforated cylinder 10 should be between one-half and two inches in diameter since it is essential to have sufficient fuel of the heat required.

The fuel distribution system comprises one or more tubes 101 connected to the manifold assembly 16 which is connected to the propane bottle. As shown, the tube 101 extends through the spaced cylinder 102 into the fuel chamber 100 of the catalytic heating chamber. The end of the tube contains a precision orifice sized to deliver between 5,000 BTU/hr to 80,000 BTU/hr when using natural gas (methane), propane, butane or mixtures thereof. An fuel igniter 104 located in the pilot light assembly 18 is provided to heat the catalytic pad 6 to auto ignition temperature of the fuel in the fuel chamber. More detail of the fuel manifold 16 is shown in FIG. 3. The main fuel line 200 is connected to the fuel tank (not shown) and thence to the inlet of the fuel manifold which comprises a three-way valve 201. There are two outlets on valve 201, one of which is connected by tubing 203 to fuel pilot 104 to provide the fuel necessary to heat the catalytic pad to auto ignition temperature. The second outlet is connected by tubing 204 to the threaded fitting 205 on the bottom of tubing 101 in fuel chamber 100. An electric igniter 206 is connected to igniter button 17 on the cabinet 30 to provide a spark to ignite the fuel pilot thereby igniting the pilot. The valve is controlled by thermocouple actuator 207 which is connected to thermocouple sensor 208 which senses the temperature of the catalyst pad when catalytic combustion is established. The pilot light ignites the fuel that has diffused through the catalytic heating chamber 110. When the temperature in the catalytic pad reaches auto ignition temperature the thermocouple actuator shuts off the fuel to the pilot 104. Control knob 17 on cabinet 19 controls the fuel flow to the manifold.

In an alternate embodiment a thin electrical heating wire (not shown) is wrapped around the insulating pad 7. The electrical heating wire is connected to a battery-operated circuit which has a control system and sensing element for the temperature of the catalyst pad. The heating pad is operated with the initial flow of gas but is shut off automatically when the temperature on the pad reaches catalytic heating ignition requirements.

Overall the surface temperature of the catalytic heating element can reach from between 500° F. and 1100° F., but the outside surface of the protective screen 1 is less than 120° F. The radiant energy produced has a wave length of between 1 and 15 microns. 

1. A patio heater comprising a cylindrical catalytic heating chamber vertically mounted on a base.
 2. The patio heater according to claim 1 wherein said cylindrical catalytic heating chamber comprises: (a) a low density ceramic pad coated with a highly dispersed oxidation catalyst; (b) a high density ceramic insulating pad; (c) said low density ceramic pad and said high density ceramic pad being rolled together to form a cylinder around the outer surface of a perforated metal cylinder to form a fuel chamber with said high density ceramic pad being located between said low density ceramic pad and said perforated metal cylinder.
 3. The patio heater according to claim 2 further comprising: (d) a cylindrical sleeve around said catalytic heating chamber, said sleeve being formed from expanded metal and having openings of from one-quarter square inch to five square inches with a total open area of from 50% to 90%; and (e) caps covering either end of said catalytic heating chamber and overlapping said sleeve and sealing said fuel chamber.
 4. The patio heater according to claim 2 wherein said oxidation catalyst is selected from the group consisting of platinum, palladium, rhodium, or cobalt oxide.
 5. The patio heater according to claim 4 wherein the oxidation catalyst is one to 10 percent platinum based upon the total weight of the low density ceramic pad.
 6. The patio heater according to claim 5 wherein said low density ceramic pad having a density of from between 1 to 8 pounds per cubic foot and the density of said high density ceramic pad being between 8 and 50 pounds per cubic foot.
 7. The patio heater according to claim 4 wherein the oxidation catalyst is one to 10 percent palladium based upon the total weight of the low density ceramic pad.
 8. The patio heater according to claim 7 wherein said low density ceramic pad having a density of from between 1 to 8 pounds per cubic foot and the density of said high density ceramic pad being between 8 and 50 pounds per cubic foot.
 9. The patio heater according to claim 4 wherein the oxidation catalyst is one to 10 percent rhodium based upon the total weight of the low density ceramic pad.
 10. The patio heater according to claim 9 wherein said low density ceramic pad having a density of from between 1 to 8 pounds per cubic foot and the density of said high density ceramic pad being between 8 and 50 pounds per cubic foot.
 11. The patio heater according to claim 4 wherein the oxidation catalyst is one to 20 percent cobalt oxide based upon the total weight of the low density ceramic pad.
 12. The patio heater according to claim 11 wherein said low density ceramic pad having a density of from between 1 to 8 pounds per cubic foot and the density of said high density ceramic pad being between 8 and 50 pounds per cubic foot.
 13. The patio heater according to claim 3 further comprising: (f) an expanded metal cylinder spaced away from and around said catalytic heating chamber forming a vapor cavity annular to said catalytic heating chamber.
 14. The patio heater according to claim 13 wherein said vapor cavity is from one-half inch to two inches in diameter outside the catalytic heating chamber.
 15. The patio heater according to claim 13 wherein said expanded metal cylinder has a porosity between 25 and 70% and a wire diameter of between 0.01 and 0.08 inches.
 16. A patio heater comprising: (a) a base comprising a cabinet for containing a fuel tank; (b) a cylindrical catalytic heating chamber vertically mounted on said base, said catalytic heating chamber comprising: (i) a low density ceramic pad coated with a highly dispersed oxidation catalyst; (ii) a high density ceramic insulating pad; (iii) said low density ceramic pad and said high density ceramic pad being rolled together to form a cylinder around the outer surface of a perforated metal cylinder to form a fuel chamber with said high density ceramic pad being located between said low density ceramic pad and said perforated metal cylinder; (c) a cylindrical sleeve around said catalytic heating chamber, said sleeve being formed from expanded metal and having openings of from one-quarter square inch to five square inches with a total open area of from 50% to 90%; (d) caps covering either end of said catalytic heating chamber and overlapping said sleeve and sealing said fuel chamber to form said catalytic heating chamber; and (f) an expanded metal cylinder spaced away from and around said catalytic heating chamber forming a vapor cavity annular to said catalytic heating chamber said vapor cavity being from one-half inch to two inches in diameter outside the catalytic heating chamber.
 17. The patio heater according to claim 16 wherein said oxidation catalyst is one to 10 percent platinum based upon the total weight of the low density ceramic pad of material selected from the group consisting of platinum, palladium, rhodium, or one to 20 percent cobalt oxide based upon the total weight of the low density ceramic pad cobalt oxide. 